The first public mobile radio systems were introduced in the late 1970's and early 1980's. As a group, those now well-known systems were referred to as “first generation” systems. They included the “Advanced Mobile Phone System” (AMPS) in the United States, “Nordic” in Scandinavia, “Total Access Communications System” (TACS) in Britain, and “Nippon Mobile Telephone System” (NAMTS) in Japan. They had certain transmission characteristics that were generally common to all, such as analog frequency modulation at the radio and digital control at the network. Otherwise, however, each system used a communication standard unique to itself in comparison to the others.
The so-called “second generation” mobile radio systems began their introductions in the mid- to late-1980's. The first of these was the “Group Special Mobile” (GSM) system which became the standard in Europe. The United States followed with “Digital AMPS” (DAMPS), the TDMA version of which was sometimes referred to by its standardization name, “IS-54.” The Japanese second generation system was called “Personal Digital Cellular” (PDC). Each of these systems had their own peculiar transmission characteristics and channel conditioning.
Presently, a number of initiatives are being proposed for the “third generation” of mobile radio systems. European third generation system research is being coordinated by the “Universal Mobile Telephone System” (UMTS) initiative, which is studying various proposals including wide-band CDMA (WCDMA), improved TDMA, hybrids, etc. Japanese initiatives for third generation are called “IMT-2000” and are focusing on wide-band CDMA. “Future Public Land Mobile Telecommunications System” (FPLMTS) is another proposed third generation network.
Mobile phones for the third generation systems will be intelligent multi-mode terminals for communication with first, second and/or third generation systems. A basic problem arises, however, in designing the third generation systems in that they must be backward compatible with all second generation systems. If a third generation system is to communicate solely with a like kind of second generation system, the modifications may be straightforward. However, cooperation between countries employing disparate second generation systems is increasing. The European standards organization, ETSI, and the Japanese standards organizations, TTC and ARIB, are suggesting hand-off capability for third generation systems to both the European second generation system (GSM) and the Japanese second generation system (PDC).
PDC and GSM protocols (as well as other second generation systems) are unique to each other. GSM as well as PDC, specifies frequencies (f) and time slots (TS) in a way unique to each system, second generation systems employing CDMA specify appropriate codes, and other second generation systems use other kinds of protocol specifications. These protocols for second generation systems are well-known throughout the industry. In the example case of PDC and GSM compatibility to third generation UTMS, the PDC and GSM specifications can be adapted to provide forward compatibility. So too can UMTS specifications be adapted for backward compatibility. In the case of UMTS, however, the standard will have to be compatible to multiple different kinds of second generation communications protocols, depending upon the type of second generation system a UMTS network is in communication with at any given time.
The problem is particularly keen as it relates to hand-off procedures. As a mobile radio is handed off from a UMTS service area to a PDC service area, for example, the protocol change must be accommodated from the third generation system characteristics to the PDC second generation characteristics. The same would be true if the mobile radio signal connection was handed from a UMTS system to any other second generation system. Thus, in the above example, the UMTS would be required to communicate to PDC networks in a PDC compliant protocol, to a GSM network in a GSM compliant protocol, etc. The third generation system ends up supporting multiple mechanisms, namely PDC and GSM (among potentially others).
Previously, when systems were upgraded from first generation to second generation, backward compatibility was an issue that was addressed. Handoff techniques from, for example, analog signaling to digital signaling, were accommodated through various techniques. Such techniques included, for example, signal acquisition, modulation, and re-alignment (re-synchronization) aspects. These techniques were thus highly content-specific, requiring newer generational system to be fully, substantively conversant with previous generational systems. Content-specific AMPS to DAMPS handovers were also developed to accommodate first generation to second generation system upgrading. Such prior handoff systems did not address the problems associated with handing off signals from a new generation of system to multiple different kinds of previous generation systems.
The technology disclosed herein provides a highly efficient way of ensuring that handoffs from third generation systems to multiple different kinds of second generation systems is done efficiently and without disruption. Thus, for example, third generation UMTS systems can ensure communication with any kind of second generation system, including DAMPS, GSM, PDC, etc.
In accordance with a preferred example embodiment, a generic mechanism is provided to accommodate inter-system handovers between third generation systems and any other type of system including any type of second generation system. The generic mechanism includes a standardized data “container” structure that will include whatever information is necessary to specify a communication to a neighboring cell system in the communication language (whether common or foreign) of that neighboring cell system. Thus, for example, if a handover to a GSM neighboring cell is to occur, the container may specify the communication parameters for a GSM transmission. On the other hand, if the neighboring cell is PDC specific, the container may specify the communication parameters for a PDC transmission. Any other types of third, second, first, or other communication parameters can also be specified in the container. Using the container, the recipient of the handover can specify the communication parameters to the mobile radio, and the mobile radio can specify its capabilities to the neighboring cell using the proper parameters. Importantly, the current cell (for example, third generation) need not read and interpret the content of the particular second generation parameters in the container, provided it simply delivers the container to the neighboring cell for evaluation. In this way, the third generation system need not understand all previous generation protocols and the recipient second (or first) generation system is fooled into believing that it is communicating with another second (or first) generation system.